The only thing I know about Squid is that it is an internet proxy. How does it selectively block internet access without knowning the clients IP address (DHCP would issue different addresses each day). Can it block by MAC address? From the email point of view, I can see that it could block by the sender's address, but I am at a loss as to how it would block internet access.
While your point about going to another PC to gain access is valid, unless they log into that PC using their credentials, I don't know how access could be prevented.
Frankly, I find that the restrictions make my job excessively difficult, it would be better to have the ability to view what is being accessed on the web by each computer. Does Squid have a UI that makes viewing by computer easy or is there add-on tools to view the logs and cache by machine name, MAC or IP?
Steve.